The calculation of the y-component is similar to that of the x. The only difference is that the y-component of vector A is AB instead of OB. So, we will have a $$\sin$$ instead of a $$\cos$$.
That is, the y-component, which is nothing but the length AB, is
$$\mathrm{AB} = \mathrm{OA} \times \mathrm{sin} \, 30^{\circ} = 10 \times \mathrm{sin} \, 60^{\circ}$$